Chief electrician Antonio Muscas told the court that the “emergency generator didn't work”, according to a report in La Repubblica, the Italian daily.
“We used a screwdriver to try to flip the switch on, but we only got it to work for a few minutes,” he said.
The cruise ship’s captain, Francesco Schettino, is currently on trial for multiple manslaughter. Dubbed "Italy's most hated man" by the tabloids, he is accused of sailing too fast and too close to Giglio island in a risky manoeuvre to "salute" the residents, an Italian maritime tradition.
The generator operates lifeboat pulleys, but the main electrical board was flooded minutes after the ship hit the rocks, Muscas said.
The court also heard the recording of a conversation between Schettino and chief engineer Giuseppe Pilon that took place on the night, which proves Schettino knew the ship was lost just six minutes after impact.
''So we're sinking, is that it? I'm not clear on what's going on'', said Schettino.
''Yes, the water has come up to the central machine room'', Pilon answered.
The 290-metre Concordia crashed into rocks on the night of January 13th, 2012, with 4,229 people from 70 countries on board.
Schettino, who has been nicknamed "Captain Coward" for apparently heading ashore while terrified people were still trapped aboard, faces up to 20 years in prison if he is convicted.
Five suspects, including the director of ship owner Costa Crociere's crisis unit, have already been sentenced to jail in plea bargain deals.